Role of the antibody Fc in the immune clearance of Trypanosoma cruzi.

Passive transfer of immune serum obtained from mice chronically infected with Trypanosoma cruzi to mice containing circulating bloodstream trypomastigotes induces a very fast clearance of the parasites. Comparison of trypomastigotes clearance in normocomplementemic and C5-deficient mice showed no difference. IgG fraction obtained from immune serum was very efficient at inducing complement-mediated lysis and immune clearance of bloodstream trypomastigotes, whereas its Fc-missing F (ab') 2 fragments, although able to induce lysis, were unable to induce clearance. It is suggested that the immune clearance of bloodstream trypomastigotes is dependent on the antibody Fc region and that complement-mediated lysis is not a prerequisite for elimination of the parasites from circulation.